Devices for exploiting the forces developed by the inertia of flowing liquid which has been decelerated (the "water hammer" effect) have been proposed in the past. The most common application of such devices has been in well drilling tools.
Typically, prior devices have involved liquid driven hammers which impact against anvils, which in turn impact against the work piece. That is to say, the water hammer force has been applied to the work indirectly. The resetting of the flow decelerating valve has usually been accomplished by reliance on springs calculated to act during the period of rarefaction or reduced pressure in the liquid which follows promptly after the inertia surge. See U.S. Pat. Nos. 699,273; 842,049 and 1,112,498. Spring resetting of the flow interrupting valve has several disadvantages as a mode of operation. The period of rarefaction in the liquid during which the valve must be opened is quite short in duration, and it is accordingly difficult to assure adequate opening.
In such devices a lack of operating flexibility is inherent, because once a valve spring of a given strength is selected and installed, the maximum and minimum operating pressures of the unit are fixed.
For these and similar reasons, there has been a sparcity of attempts to apply the liquid inertia impact principle to other areas where an abrupt application of force is required, such as pile driving, both on land and under sea, punch pressing, baling presses, seismic noise-makers, and the like.